Image processing apparatus, image processing method, and program

ABSTRACT

An image processing apparatus has an acquisition unit which acquires a second tomogram related to a first tomogram of an eye to be examined based on position information of an eye fundus of the eye to be examined according to a predetermined rule; and a display control unit which displays the first tomogram and the second tomogram on a display unit.

This application is a continuation of application Ser. No. 13/319,879filed Nov. 10, 2011, which was the National Stage of InternationalPatent Application No. PCT/JP2010/060919 filed Jun. 21, 2010.

TECHNICAL FIELD

The present invention relates to an image processing technique thatassists image processing of an eye portion and, more particularly, to animage processing apparatus, image processing method, and program, whichexecute image processing using tomograms of an eye portion.

BACKGROUND ART

A tomography apparatus for an eye portion such as an OCT (OpticalCoherence Tomography) allows to three-dimensionally observe the state ofthe interior of retina layers. In recent years, this tomographyapparatus for an eye portion has received a lot of attention since it iseffective to give more adequate diagnoses of diseases.

FIG. 3A illustrates tomograms of a retina captured by the OCT. Referringto FIG. 3A, reference symbols T₁ to T_(n) denote two-dimensionaltomograms (B-scan images) of a macular region. Reference symbol Ddenotes an optic nerve papilla; and M, a macular region. Referencenumeral 1 denotes an inner limiting membrane; 2, a boundary between anerve fiber layer and its underlying layer (to be referred to as a nervefiber layer boundary 2 hereinafter); and 2′, a nerve fiber layer.Reference numeral 3 denotes a boundary between an inner plexiform layerand its underlying layer (to be referred to as an inner plexiform layerboundary 3 hereinafter); and 4, a boundary between an outer plexiformlayer and its underlying layer (to be referred to as an outer plexiformlayer boundary 4 hereinafter). Reference numeral 5 denotes a junctionbetween inner and outer photoreceptor segments; 6, a retinal pigmentepithelial layer boundary; and 6′, a retinal pigment epithelial layeredge. For example, when such tomograms are input, if the thickness (TT1in FIG. 3A) of the nerve fiber layer 2′ can be measured, a degree ofprogress of a disease such as glaucoma and a recovery level after amedical treatment can be quantitatively diagnosed. In order to judge theprogress states and recovery levels of medial treatment effects ofdiseases of an eye portion, a technique which facilitates comparisonoperations using a display mode that allows an operator to recognize themutual relationship between a fundus image and tomograms obtained by theOCT has been disclosed (see Japanese Patent Laid-Open No. 2008-073099).

However, Japanese Patent Laid-Open No. 2008-073099 described abovedisplays an OCT tomogram and layer boundaries corresponding to aposition designated on a fundus image, but it merely displays a tomogramand its boundaries at a position designated by a doctor. For thisreason, the doctor may often dither to judge about whether a portionhaving an abnormal layer thickness in the tomogram at the designatedposition is caused by an individual feature or a disease.

SUMMARY OF INVENTION

According to one aspect of the present invention, there is provided animage processing apparatus comprising: acquisition means for acquiring asecond tomogram related to a first tomogram of an eye to be examinedbased on position information of an eye fundus of the eye to be examinedaccording to a predetermined rule; and display control means fordisplaying the first tomogram and the second tomogram on display means.

According to the present invention, a plurality of tomograms atstructurally symmetric positions in a single eye to be examined aregenerated, and are displayed to be juxtaposed in a comparable state.Thus, the operator can easily judge whether information obtained fromthe tomograms is caused by an individual difference or a disease upongiving a diagnosis with reference to the tomograms.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the functional arrangement of an imageprocessing system according to the first embodiment;

FIGS. 2A and 2B are flowcharts showing the processing sequence of animage processing apparatus according to the first embodiment;

FIGS. 3A and 3B are views showing an example of tomograms and aprojected image according to the first embodiment;

FIGS. 4A, 4B, and 4C are views for explaining tomogram positionsaccording to the first embodiment;

FIG. 5 is a view showing a display example of tomograms according to thefirst embodiment;

FIG. 6 is a block diagram showing the functional arrangement of an imageprocessing apparatus according to the second embodiment;

FIGS. 7A and 7B are flowcharts showing the processing sequence of theimage processing apparatus according to the second embodiment;

FIGS. 8A, 8B, and 8C are views showing difference information displayexamples at structurally symmetric positions according to the secondembodiment;

FIGS. 9A and 9B are views showing tomogram display examples in whichdifferences are detected according to the second embodiment; and

FIG. 10 is a block diagram showing the functional arrangement of animage processing apparatus according to the third embodiment.

DESCRIPTION OF EMBODIMENTS First Embodiment

The arrangement of an image processing apparatus according to thisembodiment will be described below with reference to FIG. 1. An imageprocessing apparatus 10 sets a reference tomographic plane indicating atomographic plane serving as a reference of a tomogram group including aplurality of tomograms obtained by imaging those of an eye to beexamined, and generates, for example, parallel tomograms having apredetermined positional relationship based on the reference tomographicplane. The apparatus selects a tomogram at a position designated by anoperator, and a tomogram at a position structurally symmetric to thedesignated position in that eye. Then, the image processing apparatusdisplays these tomograms to be juxtaposed, thereby executing imageprocessing for assisting a process for judging whether informationobtained from the tomograms is caused by an individual difference ordisease.

Note that this embodiment will explain a case in which tomograms ofthree-dimensional data are to be acquired. However, the presentinvention is not limited to this as long as data which can constructthose at positions symmetrical about a line that couples an optic nervepapillary area and a macular region can be acquired. Also, a dataacquisition method is not particularly limited as long as data atplane-symmetric positions can be reconstructed by, e.g., interpolationprocessing from the acquired data.

The image processing apparatus 10 shown in FIG. 1 is connected to atomography apparatus 20 via an interface such as USB or IEEE1394, and isconnected to a data server 50 via a local area network (LAN) 40. Notethat the image processing apparatus 10 may be connected to theseapparatuses via an external network such as the Internet.

The tomography apparatus 20 captures tomograms of an eye portion, andincludes, for example, a time domain OCT or Fourier domain OCT. The dataserver 50 is an information processing apparatus (server) which holdstomograms, image feature amounts, and the like of an eye to be examined.The data server 50 saves tomograms of an eye to be examined output fromthe tomography apparatus 20 and analysis results output from the imageprocessing apparatus 10. Also, the data server 50 transmits previousdata associated with an eye to be examined to the image processingapparatus 10 in response to a request from the image processingapparatus 10.

The image processing apparatus 10 includes a control unit 200, eye to beexamined information acquisition unit 210, image acquisition unit 220,instruction acquisition unit 230, display unit 270, and result outputunit 280. The control unit 200 includes a first tomogram selection unit201, second tomogram selection unit 202, image generation unit 203,image processing unit 204, and image storage unit 205. The imageprocessing unit 204 includes a registration unit 241, projected imagegeneration unit 242, feature extraction unit 243, and referencetomographic plane setting unit 244, and sets a reference tomographicplane for a tomogram group (volume data). The control unit 200 generatesa plurality of tomograms based on this reference tomographic plane.

The eye to be examined information acquisition unit 210 externallyacquires information required to discriminate and identify an eye to beexamined. The image acquisition unit 220 acquires tomograms transmittedfrom the tomography apparatus 20. The instruction acquisition unit 230acquires processing instructions input by the operator. The display unit270 displays tomograms processed by the control unit 200 on a monitor.The result output unit 280 associates a date and time of examination,the information required to discriminate and identify the eye to beexamined, the tomograms of the eye to be examined, and an analysisresult obtained by the image processing unit 220 with each other asinformation to be saved, and transmits that information to the dataserver 50.

The processing sequence of the image processing apparatus 10 of thisembodiment will be described below with reference to the flowchart shownin FIG. 2A. The processes of the flowchart are implemented by executinga program stored in an internal memory (not shown) of the imageprocessing apparatus 10. The processing sequence of this embodimentacquires tomograms of an eye to be examined, and generates a projectedimage from the tomograms so as to display a broad fundus region. Thesequence sets a reference tomographic plane for the tomograms. Then, thesequence selects a plane-symmetric tomogram based on a tomogram at aposition which is designated by the operator on the projected image, andthe reference tomographic plane, and displays the selected tomograms.

In step S201, the eye to be examined information acquisition unit 210externally acquires an object identification number as informationrequired to discriminate and identify an eye to be examined. Then, theunit 210 acquires information (a name, age, gender, and the like of apatient) associated with the eye to be examined, which is held by thedata server 50, based on the object identification number.

In step S202, the image acquisition unit 220 acquires tomogramstransmitted from the tomography apparatus 20. The acquired tomogramsconfigure a tomogram group. Then, the unit 220 transmits the acquiredinformation to the image storage unit 205. The following descriptionwill be made under the condition that the tomograms acquired by theimage acquisition unit 220 are those of the eye to be examinedidentified by the eye to be examined information acquisition unit 210.

In step S203, the image processing unit 204 sets a reference tomographicplane indicating a tomographic plane serving as a reference fortomograms. The process of this step will be described in detail laterusing the flowchart shown in FIG. 2B.

In step S204, the image generation unit 203 generates tomograms from thetomogram group (volume data). In this step, the unit 203 generates thereference tomographic plane and a plurality of tomograms parallel to thereference tomographic plane. The generation process of the referencetomographic plane and tomograms will be described below with referenceto FIG. 4A. Referring to FIG. 4A, reference symbol F denotes an eyefundus; R, a rectangular region where a tomogram is obtained in the eyefundus F; and B, a one-dashed chain line indicating the position of thereference tomographic plane.

Upon generating tomograms from the tomogram group, pixels which arelocated at coordinates that are not acquired upon image capturing aregenerated by image interpolation. As a method of image interpolation,for example, a bicubic method is used to generate tomograms. Note thatthe reference tomographic plane is set in the rectangular region R inFIG. 4A. However, the present invention is not limited to such specificexample. For example, as shown in FIG. 4B, a rectangular region R′parallel to the reference tomographic plane may be set, and tomogramsmay be generated from the tomogram group within the rectangular regionR′.

In step S205, the instruction acquisition unit 230 acquires a positiondesignated by the operator on a projected image or the tomogram group.However, if no operator's instruction is acquired, the referencetomographic plane set in step S203 is used as the designated position.As a method of designating a position of interest by the operator, he orshe may directly designate a point using, e.g., a mouse, or maydesignate the position of interest by operating a slider or a mousewheel, or by inputting a distance from the reference tomographic planeas a numerical value.

In step S206, the first and second tomogram selection units 201 and 202respectively select tomograms to be displayed on the display unit 270based on the reference tomographic plane and the position acquired bythe instruction acquisition unit 230. The tomogram selection processwill be described below with reference to FIG. 4C.

In FIG. 4C, an arrow S indicates a position (x_(i), y_(j)) designated bythe operator. A broken line B1 represents a tomogram position selectedby the first tomogram selection unit 201, and a broken line B2represents that selected by the second tomogram selection unit 202.

The first tomogram selection unit 201 selects a tomogram correspondingto the designated position acquired in step S205 from the plurality oftomograms generated in step S204. The second tomogram selection unit 202selects a tomogram at a position which is plane-symmetric to thetwo-dimensional tomogram selected by the first tomogram selection unit201 with respect to the reference tomographic plane from the pluralityof tomograms generated in step S204.

In step S207, the tomograms selected in step S206 are displayed on thedisplay unit 270. FIG. 5 shows a screen display example. In FIG. 5, athree-dimensional tomogram group 501, projected image 502, tomogram 1503 at the position designated by the operator, and tomogram 2 504located at a plane-symmetric position based on the reference tomographicplane are displayed on the display unit 270. The tomogram 1 503 andtomogram 2 504 are displayed to be juxtaposed at upper and lowerpositions. The positions of the tomogram 1 503 and tomogram 2 504generated from the tomogram group are respectively displayed on theprojected image 502. Upon displaying the positions of the tomograms onthe projected image, the position of the reference tomographic plane isalso displayed, and different colors and line types of positioninformation can be used. For example, assume that a color of a linewhich represents the position of the tomogram 1 503 is red, and that ofa line which represents the position of the tomogram 2 504 is blue. Notethat color settings, line types, ON/OFF of position display on theprojected image, and the like can be changed using a user interface (notshown).

When the position of the tomogram 1 503 is changed, the second tomogramselection unit 202 displays the tomogram 2 504 at a positioncorresponding to the changed tomogram 1 503. As a display method, whenthe position of the tomogram 1 503 is continuously changed using, e.g.,a slider or mouse, the position of the tomogram 2 504 is alsosynchronously and continuously changed and displayed. Alternatively,while the position of the tomogram 1 503 is continuously changed, theposition of the tomogram 2 504 is left unchanged, and when the positionof the tomogram 1 503 is settled, a tomogram at a positionplane-symmetric to the tomogram 1 503 may be selected and displayed.

In step S208, the instruction acquisition unit 230 externally acquiresan instruction as to whether or not to end the tomogram analysisprocessing by the image processing apparatus 10. This instruction isinput by the operator using a user interface (not shown). If theoperator designates a position of interest for the tomogram group ortwo-dimensional tomogram without ending the processing, the processreturns to step S204. If the instruction to end the processing isacquired, the image processing apparatus 10 ends its processing.

The reference tomographic plane setting process in step S203 will bedescribed below with reference to FIG. 2B.

In step S210, the registration unit 241 registers the positions amongtomograms T₁ to T_(n). The unit 241 defines an evaluation function thatrepresents a similarity between two tomograms in advance, and deformsimages to obtain the best value of the evaluation function. As theevaluation function, a method of evaluating a similarity using pixelvalues can be used. For example, evaluation is made using mutualinformation contents. Upon deforming an image, affine transformation canbe used to attain translation and rotation and to change an enlargementfactor.

In step S220, the projected image generation unit 242 generates aprojected image by integrating respective tomograms in a depthdirection. FIGS. 3A and 3B show examples of tomograms of retina layersand a projected image. FIG. 3A shows tomograms of retina layers, andFIG. 3B shows a projected image P generated by integrating luminancevalues of the tomograms in the depth direction (z-direction). In theprojected image P, a curve v represents a blood vessel, D represents anoptic nerve papillary area, and M represents a macular region.

In step S230, the feature extraction unit 243 extracts the centers ofthe optic nerve papillary area D and macular region M from thetomograms.

An example of the method of extracting the center of the optic nervepapillary area D will be described below. In order to detect a region ofthe optic nerve papillary area D, the retinal pigment epithelial layeredge 6′ is detected in the tomogram group shown in FIG. 3A. The retinalpigment epithelial layer boundary 6 is a high-luminance region, and canbe detected using feature amounts of a filter which emphasizes layerstructures or that which emphasizes edges. Then, the retinal pigmentepithelial layer edge 6′ near an optic nerve papilla fovea is detectedfrom the retinal pigment epithelial layer boundary 6. Then, the detectedretinal pigment epithelial layer edges 6′ are coupled in athree-dimensional region to form an optic nerve papillary region. Theoptic nerve papillary region undergoes outlier removal or morphologyprocessing to define the optic nerve papillary area D. As the center ofthe optic nerve papillary area D, a barycentric position of the regionis used.

An example of the method of extracting a central fovea of the center ofthe macular region M will be described below. In order to detect thecentral fovea, the inner limiting membrane 1 is detected in the tomogramgroup shown in FIG. 3A. The inner limiting membrane 1 is also detectedusing layer or edge features as in the retinal pigment epithelial layerboundary 6. Since the central fovea has a recessed shape in a retina, itis extracted using shape features of the detected inner limitingmembrane 1. In the macular region M, since points having largecurvatures are concentrated, the curvatures are calculated at respectivepoints of the detected inner limiting membrane 1, and an overall regionwhere the points with the large curvatures are concentrated isextracted. In the extracted region, a portion which is located at adeepest portion in the three-dimensional tomogram is detected as thecentral fovea.

In step S240, the reference tomographic plane setting unit 244 sets aplane including a line that couples the centers of the optic nervepapillary area D and macular region M extracted by the featureextraction unit 243 as the reference tomographic plane.

In a three-dimensional space, a plane can be calculated from arbitrarythree points on the space and an equation of plane ax+by+cz+d=0.Therefore, the reference tomographic plane can be set based on twoarbitrary different points located on the line that couples the centersof the optic nerve papillary area D and macular region M, and one pointlocated at a position perpendicular to these points in the z-direction.

In the reference tomographic plane setting process, the process forautomatically setting the reference tomographic plane has beendescribed. However, the reference tomographic plane need not always beautomatically set, but it may be set at a position designated by theoperator. For example, the operator may set the central positions of theoptic nerve papillary area and macular region, or may modify thereference tomographic plane set by the computer.

This embodiment has explained the processing for setting the referencetomographic plane in the retina of the eye to be examined in advance,generating tomograms parallel to the reference tomographic plane, andthen designating a tomogram. However, the present invention is notlimited to this. For example, the following processing may be executed.A plurality of tomograms at arbitrary positions and in arbitrarydirections are generated in advance from a tomogram group (volume data)of a retina, which is captured in advance. A tomogram corresponding to aposition designated by the operator is selected from the generatedtomograms. A tomogram which is located at a position symmetric to thedesignated tomogram with respect to the reference tomographic plane isgenerated from the tomogram group of the retina, which is captured inadvance, and the designated tomogram and the generated tomogram may bedisplayed to be juxtaposed.

According to the aforementioned arrangement, a tomogram at a positiondesignated by the operator is selected, a tomogram at a positionstructurally symmetric to the designated position is selected, and thesetomograms are displayed to be juxtaposed. Then, when the operator givesa diagnosis with reference to the tomograms, he or she can easily judgewhether information obtained from the tomograms is caused by anindividual difference or disease.

Second Embodiment

The second embodiment will explain an arrangement when a measurementunit 245 is added to the arrangement of the first embodiment and someoperations of the feature extraction unit 243 are changed. Unlike in thefirst embodiment, a feature extraction unit 2431 extracts boundaries ofrespective layers from retina layers, the measurement unit 245 measureslayer thickness differences between a tomogram 1 and a tomogram 2 whichis structurally symmetric to the tomogram 1, and a display unit 270displays difference information indicating the difference measurementresults.

FIG. 6 is a block diagram showing the functional arrangement of an imageprocessing apparatus 11 of this embodiment. An image processing unit 206shown in FIG. 6 includes a registration unit 241, a projected imagegeneration unit 242, the feature extraction unit 2431, a referencetomographic plane setting unit 244, and the measurement unit 245. Sincethe operations of the registration unit 241, projected image generationunit 242, and reference tomographic plane setting unit 244 are the sameas those in the first embodiment, a description thereof will not berepeated.

The processing sequence of the image processing apparatus 11 of thisembodiment will be described below with reference to the flowchartsshown in FIGS. 7A and 7B. The processes of these flowcharts areimplemented by executing a program stored in an internal memory (notshown) of the image processing apparatus 11. Note that steps other thansteps S730, S707, and S708 are the same as those in the firstembodiment, and a description thereof will not be repeated.

In step S707 in FIG. 7A, the measurement unit 245 measures thethicknesses of respective layers based on the layer boundaries detectedin step S730. Then, the unit 245 measures differences between the layerthicknesses of tomograms 1 and 2. Alternatively, the unit 245 maymeasure differences between data in a standard database registered in adata server 50 and the thicknesses of respective layers.

In step S708, the display unit 270 displays difference information ofthe layer thicknesses (the distribution of layer structures) calculatedin step S707 together with a tomogram selected in step S706. FIGS. 8A,8B, and 8C show measurement examples of differences between nerve fiberlayers 2′ in the tomograms 1 and 2, that is, display examples ofdifferences between layer thicknesses.

In a reference tomographic plane setting process, in step S730 in FIG.7B, the feature extraction unit 2431 extracts the centers of an opticnerve papillary area D and macular region M, and extracts respectivelayers from retina layers. In the same manner as in step S230 of thefirst embodiment in which an inner limiting membrane 1 and retinalpigment epithelial layer boundary 6 are detected, the feature extractionunit 2431 detects a nerve fiber layer boundary 2, inner plexiform layerboundary 3, outer plexiform layer boundary 4, and junction 5 betweeninner and outer photoreceptor segments in this step.

Not all of the boundaries of the illustrated respective layers need bedetected, and an operator may select types of layers to be detected viaa user interface (not shown), or types of layers to be detected may beselected according to the type of an eye disease or a degree of disease.

FIG. 8A shows an example in which the thickness difference informationis superimposed on the nerve fiber layer 2′ of the tomogram 2. Diff1represents a portion where the nerve fiber layer 2′ of the tomogram 2becomes thicker than the tomogram 1, and Diff2 represents a portionwhere the nerve fiber layer 2′ of the tomogram 2 becomes thinner thanthe tomogram 1. Depending whether the layer displayed in the tomogram 2becomes thicker or thinner than that displayed in the tomogram 1, theymay be displayed using different colors, pattern types, or densities.FIG. 8B shows an example in which a tomogram 1 801, tomogram 2 802, andthickness difference graph 803 are displayed to be juxtaposed. Thethickness difference graph expresses whether the layer thicknessdisplayed in the tomogram 2 is thicker or thinner with reference to thetomogram 1. FIG. 8C shows an example in which difference informationbetween a lower region R1′ and upper region R2′ divided to have areference tomographic plane B as a boundary is superimposed on aprojected image. FIG. 8C shows an example in which a rectangular regionR′ is divided into some small regions, and difference informationbetween thicknesses in these regions is displayed. A maximum value,average value, median, minimum value, and the like of differences in therectangular region may be displayed as numerical values, or may bedisplayed using colors. For example, the operator may be allowed tojudge thickness changes based on colors: a portion with no thicknesschange may be displayed in green, a thinner portion may be displayed inblue, and so forth. When differences are displayed using colors, theymay be displayed for respective pixels using different colors inaddition to divided small regions.

FIGS. 9A and 9B show image display examples of tomograms whendifferences are detected between the tomograms 1 and 2. FIG. 9A shows anexample in which portions where large differences are detected aredisplayed as a list, that is, display regions of the tomograms 1 and 2are separately displayed as a list. FIG. 9B shows a comparison displayexample of portions where large differences are detected, that is, thetomograms 1 and 2 are displayed to be juxtaposed. The screens shown inFIGS. 9A and 9B and that shown in FIG. 5 may be displayed selectively orsimultaneously using independent windows.

According to the aforementioned arrangement, together with a tomogram ata position designated by the operator, a tomogram at a positionstructurally symmetric to the designated position in the same eye isdisplayed to be juxtaposed, and difference information of layerthicknesses between the displayed tomograms is also displayed. Since thedifferences between the layer thicknesses of the structurally symmetricportions are displayed using numerical values, colors, or a graph, theoperator can easily make a judgment upon giving a diagnosis withreference to the tomograms.

Third Embodiment

In this embodiment, a control unit 208 includes a first image generationunit 211 and second image generation unit 212, and does not include thefirst tomogram selection unit 201 and second tomogram selection unit 202unlike in the control unit 207 of the second embodiment. In thisembodiment, a tomogram at an arbitrary position and in an arbitrarydirection designated by an operator is generated in real time from atomogram group (volume data) of a retina of an eye to be examined, whichis captured in advance. Then, a tomogram which is plane-symmetric tothat tomogram with respect to a reference tomographic plane isgenerated, and these tomograms are displayed to be juxtaposed. In thiscase, since images need not be generated in advance, a memory sizerequired to store images can be reduced, and the processing timerequired until a first tomogram is displayed can be shortened.

FIG. 10 is a block diagram showing the functional arrangement of animage processing apparatus 12 of this embodiment. Since the arrangementother than the first and second image generation units 211 and 212 inFIG. 10 is the same as that of the second embodiment, a descriptionthereof will not be repeated.

The first image generation unit 211 generates, in real time, a tomogramat a position and in a direction designated by the operator from atomogram group (volume data) of a retina, which is captured in advance.The second image generation unit 212 generates a tomogram which has aplane symmetry relationship with the tomogram generated by the firstimage generation unit 211 with respect to the reference tomographicplane. A display unit 270 displays the tomograms generated by the firstand second image generation units 211 and 212 to be juxtaposed.

According to the arrangement of this embodiment, a tomogram at aposition designated by the operator is acquired, a tomogram at aposition structurally plane-symmetric to the designated position isacquired, and these tomograms are displayed to be juxtaposed. Then, whenthe operator gives a diagnosis with reference to the tomograms, he orshe can easily judge whether information obtained from the tomograms iscaused by an individual difference or disease.

Other Embodiments

Aspects of the present invention can also be realized by a computer of asystem or apparatus (or devices such as a CPU or MPU) that reads out andexecutes a program recorded on a memory device to perform the functionsof the above-described embodiment(s), and by a method, the steps ofwhich are performed by a computer of a system or apparatus by, forexample, reading out and executing a program recorded on a memory deviceto perform the functions of the above-described embodiment(s). For thispurpose, the program is provided to the computer for example via anetwork or from a recording medium of various types serving as thememory device (e.g., computer-readable medium).

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2009-166181, filed Jul. 14, 2009, which is hereby incorporated byreference herein in its entirety.

The invention claimed is:
 1. A processing apparatus for use intomography, the processing apparatus comprising: a processor-implementedcomparison unit configured to compare, based on volume data including aplurality of tomograms obtained using optical coherence tomography,values regarding layer thicknesses at symmetrical positions with respectto a line that couples, in a fundus, a macular region and an optic nervepapillary region; and a display control unit configured to cause adisplay unit to display, on a two-dimensional image indicatingtwo-dimensional positional relations of the symmetrical positions,information indicating a comparison result produced by the comparisonunit, wherein the comparison unit automatically obtains, as thecomparison result, a difference between the values regarding layerthicknesses at symmetrical positions with respect to the line thatcouples the macular region and the optic nerve papillary region, whereinthe display control unit causes the display unit to change the displayform in accordance with the difference between the values regardinglayer thicknesses at the symmetrical positions with respect to the linethat couples the macular region and the optic nerve papillary region,and wherein the display form includes a display color.
 2. The apparatusaccording to claim 1, wherein the comparison unit is configured tocompare layer thicknesses in small regions located at symmetricalpositions with respect to the line that couples the macular region andthe optic nerve papillary region, and wherein the small regions aredefined by (i) the line that couples the macular region and the opticnerve papillary region, and (ii) a plurality of lines parallel to theline that couples the macular region and the optic nerve papillaryregion, and (iii) a plurality of lines perpendicular to the line thatcouples the macular region and the optic nerve papillary region.
 3. Theapparatus according to claim 2, wherein, for each small region, thelayer thickness is an average value of layer thicknesses obtained fromthe small region.
 4. The apparatus according to claim 3, wherein thedisplay control unit causes the display unit to display (i) the linethat couples the macular region and the optic nerve papillary region,(ii) the plurality of lines parallel to the line that couples themacular region and the optic nerve papillary region, and (iii) theplurality of lines perpendicular to the line that couples the macularregion and the optic nerve papillary region, and wherein the displaycontrol unit causes the display unit to display information indicatingthe comparison result corresponding to each small region.
 5. Theapparatus according to claim 4, wherein the display control unit causesthe display unit to display the information indicating the comparisonresult corresponding to each small region, at a position correspondingto the small region.
 6. The apparatus according to claim 2, wherein thedisplay control unit causes the display unit to display an image showinga surface of the fundus and (i) the line that couples the macular regionand the optic nerve papillary region, (ii) the plurality of linesparallel to the line that couples the macular region and the optic nervepapillary region, and (iii) the plurality of lines perpendicular to theline that couples the macular region and the optic nerve papillaryregion by superimposing (i) the line that couples the macular region andthe optic nerve papillary region, (ii) the plurality of lines parallelto the line that couples the macular region and the optic nervepapillary region, and (iii) the plurality of lines perpendicular to theline that couples the macular region and the optic nerve papillaryregion, on the image showing the surface of the fundus.
 7. The apparatusaccording to claim 2, wherein the display control unit causes thedisplay unit to display (i) the line that couples the macular region andthe optic nerve papillary region, and (ii) the plurality of linesparallel to the line that couples the macular region and the optic nervepapillary region, and (iii) the plurality of lines perpendicular to theline that couples the macular region and the optic nerve papillaryregion, and wherein the display control unit causes the display unit todisplay information indicating the comparison result corresponding toeach small region.
 8. The apparatus according to claim 7, wherein thedisplay control unit causes the display unit to display the informationindicating the comparison result corresponding to each small region, ata position corresponding to the small region.
 9. The apparatus accordingto claim 7, wherein the line that couples, in the fundus, the macularregion and the optic nerve papillary region, is a line that couples, inthe fundus, a center of the macular region and a center of the opticnerve papillary region.
 10. The apparatus according to claim 2, whereinthe display control unit causes the display unit to display an imageshowing a surface of the fundus and (i) the line that couples themacular region and the optic nerve papillary region, (ii) the pluralityof lines parallel to the line that couples the macular region and theoptic nerve papillary region, and (iii) the plurality of linesperpendicular to the line that couples the macular region and the opticnerve papillary region by superimposing (i) the line that couples themacular region and the optic nerve papillary region, (ii) the pluralityof lines parallel to the line that couples the macular region and theoptic nerve papillary region, and (iii) the plurality of linesperpendicular to the line that couples the macular region and the opticnerve papillary region, on the image showing a surface of the fundus,and wherein the display control unit causes the display unit to displaythe information indicating the comparison result corresponding to eachsmall region by superimposing the information indicating the comparisonresult corresponding to each small region on the image showing thesurface of the fundus.
 11. The apparatus according to claim 1, whereinthe line that couples, in the fundus, the macular region and the opticnerve papillary region, is a line that couples, in the fundus, a centerof the macular region and a center of the optic nerve papillary region.12. The apparatus according to claim 1, wherein the values regardinglayer thicknesses at symmetrical positions include an average value. 13.The apparatus according to claim 12, wherein the line that couples, inthe fundus, the macular region and the optic nerve papillary region, isa line that couples, in the fundus, a center of the macular region and acenter of the optic nerve papillary region.
 14. A processing apparatusfor use in tomography, the processing apparatus comprising: aprocessor-implemented comparison unit configured to compare, based on avolume data including a plurality of tomograms obtained using opticalcoherence tomography, values regarding layer thicknesses at symmetricalpositions with respect to a line that couples, in a fundus, a macularregion and an optic nerve papillary region; and a display control unitconfigured to cause a display unit to display, on a two-dimensionalimage indicating two-dimensional positional relations of the symmetricalpositions, information indicating a comparison result produced by thecomparison unit, wherein the comparison unit automatically compareslayer thicknesses in small regions located at symmetrical positions withrespect to the line that couples the macular region and the optic nervepapillary region, and wherein the small regions are defined by (i) theline that couples the macular region and the optic nerve papillaryregion, and (ii) a plurality of lines parallel to the line that couplesthe macular region and the optic nerve papillary region, and (iii) aplurality of lines perpendicular to the line that couples the macularregion and the optic nerve papillary region.
 15. The apparatus accordingto claim 14, wherein, for each small region, the layer thickness is anaverage value of layer thicknesses obtained from the small region. 16.The apparatus according to claim 14, wherein the display control unitcauses the display unit to display an image showing a surface of thefundus and (i) the line that couples the macular region and the opticnerve papillary region, (ii) the plurality of lines parallel to the linethat couples the macular region and the optic nerve papillary region,and (iii) the plurality of lines perpendicular to the line that couplesthe macular region and the optic nerve papillary region by superimposing(i) the line that couples the macular region and the optic nervepapillary region, (ii) the plurality of lines parallel to the line thatcouples the macular region and the optic nerve papillary region, and(iii) the plurality of lines perpendicular to the line that couples themacular region and the optic nerve papillary region, on the imageshowing the surface of the fundus.
 17. The apparatus according to claim14, wherein the display control unit causes the display unit to display(i) the line that couples the macular region and the optic nervepapillary region, and (ii) the plurality of lines parallel to the linethat couples the macular region and the optic nerve papillary region,and (iii) the plurality of lines perpendicular to the line that couplesthe macular region and the optic nerve papillary region, and wherein thedisplay control unit causes the display unit to display informationindicating the comparison result corresponding to each small region. 18.The apparatus according to claim 14, wherein the display control unitcauses the display unit to display the information indicating thecomparison result corresponding to each small region, at a positioncorresponding to the small region.
 19. The apparatus according to claim14, wherein the display control unit causes the display unit to displayan image showing a surface of the fundus and (i) the line that couplesthe macular region and the optic nerve papillary region, (ii) theplurality of lines parallel to the line that couples the macular regionand the optic nerve papillary region, and (iii) the plurality of linesperpendicular to the line that couples the macular region and the opticnerve papillary region by superimposing (i) the line that couples themacular region and the optic nerve papillary region, (ii) the pluralityof lines parallel to the line that couples the macular region and theoptic nerve papillary region, and (iii) the plurality of linesperpendicular to the line that couples the macular region and the opticnerve papillary region, on the image showing the surface of the fundus,and wherein the display control unit causes the display unit to displaythe information indicating the comparison result corresponding to eachsmall region by superimposing the information indicating the comparisonresult corresponding to each small region on the image showing thesurface of the fundus.
 20. The apparatus according to claim 7, whereinthe line that couples, in the fundus, the macular region and the opticnerve papillary region, is a line that couples, in the fundus, a centerof the macular region and a center of the optic nerve papillary region.21. The apparatus according to claim 14, wherein the display controlunit is configured to change the display form of the informationindicating the comparison result in accordance with the comparisonresult.
 22. The apparatus according to claim 14, wherein the valuesregarding layer thicknesses at symmetrical positions include an averagevalue.
 23. A non-transitory computer-readable storage medium storing acomputer program which instructs a computer to execute a method ofcomparing layer thicknesses for use in tomography, the methodcomprising: a comparison step of comparing, based on a volume dataincluding a plurality of tomograms obtained using optical coherencetomography, values regarding layer thicknesses at symmetrical positionswith respect to a line that couples, in a fundus, a macular region andan optic nerve papillary region, and of automatically obtaining, as acomparison result, a difference between the values regarding layerthicknesses at symmetrical positions with respect to the line thatcouples the macular region and the optic nerve papillary region; and adisplay control step of displaying, on a two-dimensional imageindicating two-dimensional positional relations of the symmetricalpositions, information indicating the comparison result that is thedifference between the values regarding layer thicknesses at symmetricalpositions with respect to the line that couples the macular region andthe optic nerve papillary region, using a display form that is changedin accordance with the comparison result that is the difference betweenthe values regarding layer thicknesses at symmetrical positions withrespect to the line that couples the macular region and the optic nervepapillary region.
 24. The non-transitory computer-readable storagemedium according to claim 23, further comprising a determination step ofdetermining automatically the symmetrical positions with respect to theline that couples, in the fundus, the macular region and the optic nervepapillary region.
 25. The non-transitory computer-readable storagemedium according to claim 23, wherein the values regarding layerthicknesses at symmetrical positions include an average value.
 26. Aprocessing apparatus for use in tomography, the processing apparatuscomprising: a processor-implemented comparison unit configured tocompare, based on a volume data including a plurality of tomogramsobtained using optical coherence tomography, values regarding layerthicknesses at symmetrical positions with respect to a line thatcouples, in a fundus, a macular region and an optic nerve papillaryregion; and a display control unit configured to cause a display unit todisplay, on a two-dimensional image indicating two-dimensionalpositional relations of the symmetrical positions, informationindicating a comparison result by the comparison unit, wherein thecomparison unit automatically obtains, as the comparison result, adifference between the values regarding layer thicknesses at symmetricalpositions with respect to the line that couples the macular region andthe optic nerve papillary region, and wherein the display control unitcauses the display unit to display as the information indicating acomparison result, using a display form in accordance with thedifference between the values regarding layer thicknesses at symmetricalpositions with respect to the line that couples the macular region andthe optic nerve papillary region, information indicating the differencebetween the values regarding layer thicknesses at symmetrical positionswith respect to the line that couples the macular region and the opticnerve papillary region.
 27. A processing system for use in tomography,the system comprising: an optical coherence tomography apparatusconfigured to obtain a tomogram of a fundus of an eye to be examined;and a processing apparatus according to claim
 26. 28. The systemaccording to claim 27, further comprising a processor-implementeddetermination unit which is configured to extract the macular region andthe optic nerve papillary region from an image of the fundus of the eyeto be examined, and which is configured to determine the line thatcouples the macular region and the optic nerve papillary region based onthe extraction.
 29. The system according to claim 28, wherein the linethat couples, in the fundus, the macular region and the optic nervepapillary region, is a line that couples, in the fundus, a center of themacular region and a center of the optic nerve papillary region, andwherein the determination unit extracts the center of the macular regionand the center of the optic nerve papillary region from the image of thefundus of the eye to be examined.
 30. The system according to claim 27,wherein the display unit displays the information indicating thedifference at the symmetrical positions with respect to the line thatcouples the macular region and the optic nerve papillary region.
 31. Thesystem according to claim 27, wherein the line that couples, in thefundus, the macular region and the optic nerve papillary region, is aline that couples, in the fundus, a center of the macular region and acenter of the optic nerve papillary region.
 32. The system according toclaim 27, further comprising a processor-implemented determination unitconfigured to determine automatically the symmetrical positions withrespect to the line that couples, in the fundus, the macular region andthe optic nerve papillary region.
 33. The system according to claim 27,wherein the values regarding layer thicknesses at symmetrical positionsinclude an average value.
 34. The apparatus according to claim 26,wherein the values regarding layer thicknesses at symmetrical positionsinclude an average value.
 35. A processing apparatus for use intomography, the processing apparatus comprising: a processor-implementedcomparison unit configured to compare, based on a volume data includinga plurality of tomograms obtained using optical coherence tomography,values regarding layer thicknesses at symmetrical positions with respectto a line that couples, in a fundus, a macular region and an optic nervepapillary region; and a display control unit configured to cause adisplay unit to display, on a two-dimensional image indicatingtwo-dimensional positional relations of the symmetrical positions,information indicating a comparison result by the comparison unit,wherein the comparison unit automatically obtains, as the comparisonresult, a difference between the values regarding layer thicknesses atsymmetrical positions with respect to the line that couples the macularregion and the optic nerve papillary region, wherein the display controlunit causes the display unit to display as the information indicating acomparison result, using an appearance in accordance with the differencebetween the values regarding layer thicknesses at symmetrical positionswith respect to the line that couples the macular region and the opticnerve papillary region, the information indicating the differencebetween the values regarding layer thicknesses at symmetrical positionswith respect to the line that couples the macular region and the opticnerve papillary region, and wherein the appearance is color, patterntype, or density.
 36. The apparatus according to claim 35, wherein thevalues regarding layer thicknesses at symmetrical positions include anaverage value.